1. Field of the Invention
This invention is related to positioning using non-GPS information when a GPS only solution is not available.
2. Description of Related Art
There is a demand for technology that can determine the geographic location of cellular telephones and other devices. Conventional triangulation methods can be used to locate a transmitter by determining the direction from which signals are received by plural receivers. However, signals received from a wireless device can be relatively weak and triangulation generally requires sensitive directional equipment which must be able to distinguish individual transmitters in a network. Triangulation systems can usually locate only a few devices at any given time and large numbers of triangulation receivers would be required to enable widespread access to triangulation services. Consequently, triangulation systems tend to be economically impractical.
Global positioning systems (GPS) can accurately locate a device by triangulation-like methods involving signals received from multiple satellites. However, implementation of GPS technology in wireless devices can be expensive, may necessitate large form-factor devices and can significantly increase power consumption. Therefore, the disadvantages of providing GPS in space-constrained, cost-sensitive wireless devices deter widespread implementation.